The Photobiology Core will serve as a central facility for consolidating ultraviolet light sources and photodetectors in order to standardize their use and to more effectively maintain quality control. Specific aims of the Core are: 1) to make available and maintain artificial sources for ultraviolet radiation, 2) to insure quality control by periodic measurement of irradiance and emission spectrum from these sources using appropriate photodetectors, and 3) to provide guidance and training in the use of these light sources and photodetectors. Two major categories of services will be provided: 1) maintenance and quality control of light sources, and 2) guidance and technical training in the use of these equipment. Within each category, specific services will include ultraviolet irradiation of human subjects, of small laboratory animals, of cells or tissue under sterile conditions, and of chemicals, lipids, proteins and nucleic acids.